Harmonic frequency selector



Nov. 4, 1952 K. A. YOUNG HARMONIC FREQUENCY SELECTOR 2 SHEETS-SHEET 1 Filed April 29, 1947 kbq Nm wh R ww WA me N M K 'ATTORNEY 2 SHEETS-SHEET 2 Filed April 29, 1947 KENNETH l?. YOU/VG.

atentec ov. 4, Q

2,617,039 y HARMONIC FREQUENCY SELECTOR Kenneth A. Young, Waban, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application April 29, 1947, Serial No. 744,623

(Cl. Z50-36) 6 Claims.

This invention relates in general to apparatus for generating an electric wave having a particular frequency from selected harmonicsvof a single oscillator or a related group of oscillators, and in particular to a device for automatically selecting a proper and most advantageous combination of harmonics to provide a desired particular frequency.

In a paper published May 5, 1943, before the Wireless Section of the Institution of Electrical Engineers, London, England, and later in the Journal of the Institution of Electrical Engineers," vol. 90, part 3, December 1943, pages 165 to 180, inclusive, by H. J. Finden, there is described an apparatus for generating a desired frequency by synthesis from selected harmonics of a group of harmonics and subharmonics of a standard frequency, the apparatus yielding any frequency that is harmonically related to a multiple or a submultiple of the standard frequency. In this apparatus, the functioning of the various filters for the selection of proper harmonics, and selection of the proper sidebands when harmonies are combined, is only partly automatic, and the lack of completely automatic functioning of the synthesizer seriously limits the use thereof.

In the present invention, it is accordingly the main object to provide a computer which operates or provides information for the operation of a frequency synthesizer of the above-described kind in a, fully automatic fashion.

It is another object of this invention to provide a method and means to combine selected harmonics of a single oscillatorl or a related group of oscillators to provide an electric Wave of a desired frequency in such a fashion that electric Waves of other frequencies that may be simultaneously generated in the process of combination are spaced as far as possible in frequency from the desired wave to permit adequate filtering.

It is another object of the invention to provide means for automatically making a selection, than which there is none better, of the proper harmonics required to generate a desired frequency.

It is a further object of the invention to provide such means which is simple to operate, reliable in operation, and is constructed with a minimum of complexity.

The foregoing and other and further objects of the invention will become apparent from the following description of an exemplary embodiment thereof, reference being had to the accompanying drawings, wherein:

Fig. l illustrates in block diagram form an apparatus for generating various frequencies from selected harmonics of a single oscillator; and

Fig. 2 lillustrates in electrical scheme a device for selecting harmonics.

rlhe frequency generator illustrated in Fig. 1 is designed to provide any frequency in the band from l0 megacycles per second to 50 megacycles per second, in steps of 10 kilocycles per second. This generator is similar Iin nature to that described by Finden in the above-mentioned article, and only its essential elements and their interrelation Will be described herein. A fixed frequency oscillator I0, which may be crystal controlled, is arranged to oscillate at 1 megacycle per second. A frequency multiplier II is actuated by a portion of the output of the fixed frequency oscillator and in turn provides a l0 megacycle per second wave, multiplying the initial frequency by ten. A first frequency divider I2 is also actuated by a portion of the output of the fixed frequency oscillator IIJ, and in turn provides a wave oscillating at 0.1 megacycles per second, dividing the initial frequency by ten; A second frequency divider I3, actuated by the 0.1 megacycle per second wave from the first divider I2, further divides the initial frequency by ten to provide a Wave oscillator at 0.01 megacycle per second, or 1U kilocycles per second. There are now four sources I0 to I3, inclusive, of fixed frequencies which are related to each other in decade fashion.

Each of the decade fixed frequency sources IIJ to I3, inclusive, actuates a harmonic generator 20, 2|, 22, and 23, respectively. The harmonc generators are substantially identical in nature, but differ in that each is constructed and arranged to oscillate at a fundamental frequency which is substantially the same as the frequency of the particular decade source I0 to I3, inclusive, by Which it is actuated. Otherwise the harmonic generators may all be multivibrators, or any other kind of oscillator or amplifier that is rich in harmonics.

The tens decade harmonic generator 2I feeds into a tens decade harmonic selector SI which provides facilities for selectingY any one of the rst five harmonics of 10 megacycles per second, namely 10, 20, 30, 4U, or 50 megacycles per second. The selector may comprise a set of selective filters, each of which passes one of the desired frequencies, and is equipped with five output terminals labelled I, 2, t, 4, and 5, respectively, each terminal being for the corresponding numbered harmonic of 10 megacycles per second. lThus terminal l of the tens decade selector 3l is a 10 mc./sec. output terminal, terminal 2 is a 20 mc./sec. output terminal, and so on to terminal 5 which is the 50 rnc/sec. output terminal. The harmonic generator and selector is preferably built as a unit in which each frequency selective circuit (selective filters) is part of the generator. For an example, it may be an over-driven amplifier Whose plate circuit can be tuned (or switched) to the wanted harmonic.

Selection of the particular harmonic that is desired may be made in any fashion, and a newV method and apparatus for selecting harmonics will be described below. The harmonic that is selected is fed into a first balanced' modulator 4l through an input terminal 35.

Considering now the units decade, the units harmonic generator 20 feeds into a units harmonic selector 38, which provides the fifth, sixth, seventh, eighth, ninth, and tenth harmonics of 1 mc./sec. at correspondingly numbered terminals 5, 8, T, 8, 9, and l0, respectively. There is also a terminal labelled zero from which no signal is available, for a purpose that will appear below. A selected harmonic of l rnc/sec. is fed into a second balanced modulator 42 at an input terminal 36 thereof. In the tenths decade, a tenths harmonic selector 312 is actuated by the tenths harmonic generator 22 and provides the fifth, sixth, seventh, eighth, ninth, and tenth harmonics of 0.1 mc./sec. at correspondingly numbered output terminals 5, 8, l, 8, 9, and l0, respectively. Again there is a zero terminal at which no signal is available, and any one of these output terminals may selectively be connected to a third balanced modulator 413 at a first input terminal 37 thereof. The hundredths decade has a hundredths harmonic selector 33 which provides the fifth, sixth, seventh, eighth, and ninth harmonics of l lic/sec. at correspondingly numbered output terminals 5, 6, 1, 8, and 8, respectively, and a zero signal at a zero terminal. Any one of the output terminals of the hundredths harmonic selector 33 may be selectively connected to the third balanced modulator tBat a second input terminal 38 thereof.

Thev third balanced modulator 43 feeds its output, which consists almost entirely of two signals of which the frequencies are, respectively, the sum and. the difference of the frequencies brought in at the input terminals 31 and 38, to a first sideband filter 45. This filter has two control terminals "it and il for determining whether the lter shall furnish the sum' frequency v(-}) or the difference frequency Determination is made by furnishing a voltage to the terminal bearing the desired algebraic sign (-1-) or as will appear below. The output of the first sideband filter 85 is then fed into the second balanced modulator e2, where this output and the selected output from the units harmonic selector 30 are operated upon.

The second balanced modulator d2 also furnishes two signals which have, respectively, the sum and difference frequencies of the two input signals, and these two sum and difference frequency signals are fed into a second sideband filter 50, which in turn furnishes only one, the sum or the difference frequency, in accordance with the condition of the control terminals 5| and 52. Again a voltage is provided to the terminal bearing the desired algebraic sign or to select the desired frequency in the output. The output of the second sideband filter 50 is fed into the first balanced modulator 4l.

The first balanced modulator il furnishes two output signals having frequencies which are, respectively, the sum and the difference of the selected frequency from the tens harmonic selector and the frequency provided by the second sideband filter 58, and furnishes these two signals to a third sideband filter 55. This filter furnishes either the sum frequency or the dierence frequency as the final output frequency of the frequency generator, in accordance with which of the two control terminals 58 or 51 thereof is energized.

Each balanced modulator 4|, 42, and 43 is provided with an unbalance control terminal 8|, 62, and 63, respectively, by the energization of which the modulator is unbalanced and made to amplify only the signal fed thereinto from the energizing harmonic selector. A modulator is unbalanced when only one frequency is fed into it. that is, when a harmonic selector feeding it is set on zerof The frequency generator provides a desired frequency as follows.

Assume that an output frequency of 41.81 rnegacycles per second is desired. This frequency might be arrived at by adding the first hundredth decade harmonic or 0.01 rnc/sec. from the hundredths harmonic selector 33 and the eighth tenths decade harmonic, or 0.80 mc./sec. from the tenths harmonic selector 32 in the third balanced modulator 43, then adding the resultingr 0.81 rnc/sec. signal to the. first units harmonick or 1.0 Inc/sec. from the units harmonic selectorv 30 in the second balanced modulator 42, and finally adding the then resulting 1.81 rnc/sec. signalto the fourth tens harmonic, or 40 mc./sec. from the tens harmonic selector 3l, to yield an output frequency of 41.81 mc./sec. The sideband filters 45, 50, and 55 are all arranged to provide the sum' frequency rather than the difference frequency in each case.

The procedure just outlined has a defect in that the sum and difference frequencies existing in certain of the balanced modulators are too close together to permit clear cut separation of the two modulator output frequencies in the subsequent sideband filter. For example,v when the frequencies 0.01 mc./sec. and 0.80 mc./sec. are fed into the third balanced modulator 43, the sum frequency that results is 0.81 mc./sec., while the difference frequency is 0.79 Inc/sec., the separation being only 0.02 mc./sec. Separation of 0.81 inc/sec. and 0.79 inc/sec. in the first side band filter 45 is very difiicult. Assuming however, that 0.81 rnc/sec. can be separated, the mixture of 0.81 rnc/sec. and 1.0 mc./sec. in the second balanced modulator :i2 yields the sum frequency of 1.81 mc./sec. and the difference frequency of 0.19 rnc/sec., which are widely separate, and hence easily separated in the second sideband filter 50; but, the subsequent mixture of 1.81 mc./sec. and 40 mc./sec. in the rst balanced modulator M yields the sum frequency of 41.81 mc./sec. and the difference frequency of 38.19 rnc/sec., which again are too close together for easy separation in the third sideband filter 55.

The separation of the sum and difference fre-V quencies furnished by any one ofV the modulators' 4I, 62, or 63 should 'be at least. as great as the difference between two adjacent harmonic ordersY of the higher decade employedA to actuate the modulator. The process of synthesis of the desired frequency, 41.81 mc./sec., can be carried out.

to achieve such good separation by proper selec-r tion of sum and difference frequencies from the various modulators. To achieve the best possible sideband separation, the frequency 41.81 mc./sec. should be generated in the following manner.

Apply the ninth harmonic (0.09 mc./sec.) from the hundredths harmonic selector 33 and the ninth harmonic (0.90 mc./sec.) from the tenths harmonic selector 32 to the third balanced modulator 43, and take the difference frequency (0.81 mc./sec.) from the first sideband filter 45. The sum frequency is 0.99 mc./sec., which is 0.18 mc./sec. removedfrom 0.81 mc./sec. and from which 0.81 mc./sec. is easily separated. Then apply 0.81 mc./sec. and the ninth harmonic (9.0 mc./sec.) from the units harmonic selector 30 to the second balanced modulator 42, and take the difference frequency (8.19 mc./sec.) from the second sideband filter 50. The sum frequency in this case is 9.81 mc./sec., which is 1.62 mc./sec. removed from 8.19 mc./sec., and is easily separated therefrom. Finally apply the resulting 8.19 mc./sec. signal and the fifth harmonic (50.0 mc./sec.) from the tens harmonic selector 3| to the first balanced modulator 4I, and take the difference frequency 41.81 mc./sec. from the third sideband filter 55. The sum frequency in this last operation is 58.19 mc./sec., which is 16.38 mc./sec. removed from 41.81 mc./sec., and easily separated from the desired frequency.

If a frequency is to be generated in which one or more of the four digits used to designate the frequency is zero, the zero output terminal from the harmonic selector corresponding to a zero digit is selected, and the modulator into which that selector feeds is unbalanced. Since the particular frequency generator under discussion generates frequencies from to 50 mc./sec., the first digit is never zero, and the tens harmonic selector accordingly has no zero output terminal. A particular frequency may be designated as AB, CD, where: A is the rst digit, B is the second digit, C is the third digit, and D is the fourth digit. The conditions under which a particular modulator must be unbalanced are as follows:

l0-mc./scc. 1-mc./sec. 0.1-mc./sec. Frequency (First (Second Third Modulator) 41 Modulator)42 Mo ulator)43 AB. C0 Balanced... Balanced... Unbalanced. AB.00 do Unbalanced. AO. 00 Unbalanced.

A desired frequency may be generated with proper sideband separation by the following method. In accordance with this method, any four digit frequency AB, CD mc./sec. may be synthesized or generated from the most advantageously chosen harmonics from the following relation:

AB, CD mc.={10.00Mi[1.00Ni

(0.10Pi0.01Q)l} mc. Relation (1) (1) B=the harmonic order corresponding to the digit;

(2) B|1=the harmonic order corresponding to the digit advanced by one;

6 (3) 10-B=the harmonic order corresponding' to ten minus the digit; or (4) 10-(B+1) =the harmonic order corresponding to ten minus the digit advanced by one.

There is one important exception to this, however,

1. Harmonic order (M) of 10 mc./sec.

(1) The harmonic order corresponds to the rst digit (A) when the second (B) digit is:

(a) 5 to 9; (b) 0 followed by 0 in the third (C) and fourth (D) places.

(2) The harmonic order corresponds to the rst digit advanced by one (A+1) when the second (B) digit is:

(a) 1 to 4; (b) 0 not followed by 0 in the third (C) and fourth (D) places. I

Harmonic Order (N) of 1.0 mc./sec.

(1) The harmonic order corresponds to the second digit (B) when the second (B) digit is:

(a) 0, or 5 to 9, followed by 0 in the third (C) and fourth (D) places;

(b) 5 to 9 followed by 5 to 9 in the third (C place.

(2) The harmonic order corresponds to ten minus the second digit (10-B) when the second (B) digit is:

(a) 0 followed by 5 to 9 in the third (C) place; (b) 1 to 4 followed by 0 in both the third (C) and fourth (D) places, or by 5 to 9 in the third (C) place.

(3) The harmonic order corresponds to the second digit advanced by one (B+1) whenth second (B) digit is:

(a) 5 to 9 followed by 0 in the third (C) place but not by 0 in the fourth (D) place;

(b) 5 to 9 followed by 1 to 4 in the third (C) place.

(4) The harmonic order corresponds to ten minus the second digit advanced by one [l0-(B+1)l when the second (B) digit is:

(a) 0, or 1 to 4, followed by 0 in the third (C) place, but not by 0 in the fourth (D) place; (b) 0, or 1 to 4, followed by 1 to 4 in the third (C) place.

3. Harmonic order (P) of 0.1 mc./sec.

(1) The harmonic order corresponds to the third digit (C) when the third (C) digit is:

(a) 0 followed by 0 in the fourth (D) place: (b) 5 to 9 followed by O or 5 to 9 in the fourth (D) place.

(2) 'Ihe harmonic order corresponds to ten 7 minus the tlnrd digit (1Q-C) when the, third (C) digit is:

(a) followed by 5 to Qin the fourth (D) place; (b) 1 to 4 followed by 0 or 5 to 9 in the fourth (D) place.

(3) The harmonic order corresponds to the third` digit advanced by one (C-l-l) when the third (C) digit is:

(a) to 9 followed by l. to 4 in the fourth (D) place.

(4) The harmonic order correspondsv to ten minus the third digit advanced by one" [-(C-}-1)l when the third (C) digit is:

(a) 0 followed by l to 4 in the fourth (D) place; (b) 1 to 4' followed by 1 to 4 in the fourth (D) place.

4. Harmonic order (Q) of 0.01` nic/scc.

(l) The harmonic order corresponds to the fourth digit (D) when. the fourth (D) digit is 0, or 5 to 9.

(2) The harmonic order corresponds to ten minus the fourth digit (l0-D) when the fourth (D) digit is 1 to 4.

To determine the algebraic signs, or in Relation 1 above, the following rules apply:

The signin any position is:

(a) when the harmonic order (M, N, or P) immediately preceding it is:

(l) the digit (A, B, or C) or (2) ten minus the digit (A, B, or C) advanced by one.

(b) when the harmonic order (M, N, or P) immediately preceding it is:

(1) the digit (A, B, or C) advanced by one, or (2) ten minus the digit.

For example: 45.23 rnc/sec. is synthesized as follows:

Fig. 2 shows the schematic wiring diagram of a switching device, or harmonic computer, which automatically selects the proper harmonics, algebraic signs of filters, and balance and unbalance-of modulators in accordance with the above method by merely setting up a desired frequency on four decade dials. The proper combination is selected to yield best possible separation of all sidebands, in accordance with the rules set forth above, and the synthesizing of any one of the frequencies available from the frequency generator is` rendered very. simple; the rules do not have to be referred to.

The computer shown in Fig. 2 provides four decade ganged switch banks, A, B, C, and D, corresponding to the tens, units, tenths, and hundredths digits, respectively, of thefrequency sought to be generated, and a frequency ABCD is provided by setting up the A digit on the A decade, the B digit on the B decade, the C digit on the C decade, and the D digit on the D decade. The A decade has two switchbanks H and 12, the B decade has three switch banks 13, T4, and l5, t'ne C decade has three switch banks 16, T1, and 18, and the D decade has two switch banks 8l and 82. The switch banks are all of the type wherein any one of tenswitch contactsglabelled 0,. 1,2, 3, 4, 5, 6, 1, 8, and 9` ineach bank, may be connected to a: rotatable con-tactor,` HA, "IZA, 13A, 14A, 15A, 16A, 11A, 18A, 81A, or^ 82A to complete any one of ten circuits. Only those switch contacts are used on. each switch bank which will accomplish, the purposes of the computer as a whole.

The choice of harmonics from the tens harmonic selector 3| of Eig. 1 is'controlled by decade A, from the units harmonic selector 30 by decade B, from the tenths harmonic selector 32 byA decade C, and from the hundredths harmonic selector 33 by decade D. In each decade, the` rotatable contactors-make contact with the same switch contacts in all, the switchI banks of the; decade at: the same time.

In decade; A, the terminals of the tensA harmonic selector 3l are connected to the first and second switch banks 'Il and 12, respectively, as follows:

It will be noted that, while the first banky 1I selects a particular harmonic, or digit, the second bank l2 selects that harmonic increased by one, and in this connection it should be recalled that these two choices correspond to the two possible relations that M may bear to A in Relation 1. One or the other of the two switch banks 'Il andy '12 is connected to the rst balanced modulator 4l at the input terminal 35 thereof through a single pole double throw switch 9|, operated by a relay Rl, in a manner that will become apparent as the discussion proceeds.

Abattery (lll,- connected at one side to ground, furnishes power` to energize all the relays in Fig. 2. The battery furnishes the voltage for unbalancing the various modulators and controlling the algebraic signs, or of the various sideband filters.

In decade B, the terminals of the units harmonic selector 3!) are connected to the first and Here the first bank 'i3` selects the harmonic order N corresponding to the digit B or to ten minus the digit (B-l), while the second bank selects the harmonic order N corresponding to the digit increased by one (B4- 1), or to ten 9 minus the digit increased by one [lO-(B-l-l) l,

in accordance with the rules set forth above concerning the relationship between N and B in Relation 1. The third switch bank 15 of decade B energizes relay R| from the battery 90 when decade B is in any one of the first, second, third, or fourth switch positions.

When relay RI is energized, decade A selects a harmonic order M of 10 mc./sec. corresponding to the digit A advanced by one, and applies this selection to the first balanced modulator 4|, and, through a second single-pole, double-throw switch 92 operated by relay Rl, the negative terminal 56 of the third sideband filter 55 is energized and the third sideband filter 55 is conditioned to furnish a difference frequency. When the relay RI is deenergized, decade A selects a harmonic order M of' 10 mc./sec. corresponding to the digit A, the positive (-l-) terminal 51 of the third sideband filter 55 is energized from the battery 90, and the third sideband filter 55 furnishes a sum frequency.

'Relay R2 controls first and second singlepole double-throw switches 93 and 94, connected to the rst and third switch banks 13 and 15, respectively, of decade B. When decade B is in the "zero switch position, that is, when digit B is zero, and relay R2 is not energized, relay R| is energized through the third bank 15 of decade B and the second switch 94, and the tenth harmonic terminal of the' units selector 30 is connected to the zero position switch contact of the first bank 13 through the rst switch 93. But when, with the same setting of decade B, relay R2 is energized, the second switch 94 connects the unbalance terminal 6| of the first modulator 4| to the battery 90, to unbalance the modulator, and the first switch 93 connects the zero terminal of the units harmonic selector 30 to the "zero contact of the first bank 13 of decade B in place of the tenth harmonic terminal of that selector. The energization of relay R2 is controlled by the zero switch contact of the third switch bank 18 of decade C and another relay R5, as will be expla-ined below.

The rotatable contractors 13A and 14A of the rst and second switch banks of decade B are connected to a single-pole double-throw switch 95, which selects one of them for connection to the input terminal 36 of the second balanced modulator 42, in accordance with the condition of a third relay R3 which is similar in purpose to the first-mentioned relay RI. The third relay R3 controls two single-pole double-throw switches 95 and 06, of which the latter 96 controls the connection of one or the other of the two control' terminals 5| and 52 of the second sideband filter 50 (Fig. 1) to the battery 90. A fourth relay R4, which is energized simultaneously with the rst relay Rl, through the same switch bank 15 of decade B, controls a doublepole double-throw switch 91,y the function of which is to reverse the algebraic sign of the second s ideband lter 50 from that established by the third relay R3 under certain conditions. Energization of the third relay R3 is controlled by the third switch bank 18 of decade C in a like manner as the third switch bank 15 of decade B controls the energization of the rst relay RI.

In decade C, the terminals of the tenths harmonic selector 32 are connected to the first and secondswitch banks 16- and 11 as follows:`

From this chart it can be seen that decade C is connected to the tenths harmonic selector 32 in the same way as decade B is connected to the units harmonic selector 30. The first and second banks 16 and 11 make the same harmonic selections for digit C as the corresponding banks 13 and 14 respectively make for digit B. The fifth relay R5 controls rst and second single-pole double-throw switches |03 and |04 which correspond in function to first and second switches 93 and 94, respectively, controlled by the third relay R3. The first switch |03 connects the zero terminal of the tenths harmonic selector 32 to the zero position switch contact of the first bank 16 of decade C in place of the tenth harmonic terminal of that selector when the fifth relay R5 is energized. The second switch connects the unbalance terminal 62 of the second modulator 42 to the battery 90 and energizes the second relay R2 when the fifth relay R5 is energized and decade C is set on zero. The fifth relay R5 is energized through the second bank 82 of decade D when the fourth digit D is zero; and at the same time the same decade D switch connection connects the unbalance terminal 63 of the third modulator 43 to the battery 90.

The Vtenths harmonic selected is connected to the first input terminal 31 of the third balancedV R6 -is controlled by the second switch bank 82 of decade D, the relay being energized when the fourth, or D digit is 1, 2, 3, or 4. A seventh relay R1 is energized simultaneously with the third relay R3 through the third switchv bank 18 of decade C, and controls a doublepole double-throw switch |01 to reverse the sign of the first sideband lter 45 when the third relay R3 is energized.

In decade D, the terminals of the hundredths harmonic selector 33 are connected to the first bank 8| as follows:

Terminal of Hundredth Connected to Harmonic Swltch Contact Selector 33 The selected harmonic is brought directly to the second input terminal 3:3 of the third balanced modulator-d3.

It should be noted that, when the D digit is zero, the third modulator 43 is unbalanced, and the fifth relay R5 is energized. Energization of the fifth relay R5 sets up that relays second switch |06 so that, if the C digit is zero, the second modulator 42 is unbalanced and the second relay R2 is energized. Energization of the second relay R2 sets up that relays second switch 94 so that, if the B digit is zero, the first modulator 4| is unbalanced. The second Aand fifth relys R2 and R5 may thus aptly be'termed the zero digit relays.

'The operation of the harmonic computer of Fig. 2 can best Abe understood .further from a discussion of a few examples of specic frequencies chosen by means of .it. Consider the frequency 28.63 ina/sec., for example. Decade A is set on 2, decade B on 8, decade C .on 5, and decade D on 3. The frequency generator of Fig. 1 now furnishes 28.63 nic/sec. at the output thereof. This comesabout asffollows.

Decade VD being set Von 3, harmonic vorder indicator Q in Relation 1 is 7 (which is 10-3). The sixth relay R6 is energized, so that the second switch bank l1 of decade C is connected to the third modulator 43. Decade C being set on 6, harmonic order indicator P in Relation l is 7 (which is 6-5-1). The vthird and seventh relays R3 and Rl' are not energized, so the sign of the first sideband filter 45 is and the Afirst switch bank "I3 of decade B is connected to the second balanced modulator 42. Decade B being set on 8, harmonic order indicator N in Relation l is 8. The first and fourth relays Rl and R4 vare not energized, so the signs of the second and third sideband filters and 55 are both andthe first switch bank 1| of decade A is connected to the first modulator 4|. Decade A being set on 2, harmonic order indicator M in Relation 1 is '2. The harmonics that are combined to synthesize 28.63 inc/sec. are then, in'accordance with Relation 1,

-This yields `28.63 mc./sec., 'and the separation is fgood, las will be shown in detail below.

In the above example, the zero digit relays were not used, because there were no zeros in the frequency considered. Consider now the frequency 41.00 Ina/scc. Decade D is set on 0, so that Q is 0. The sixth relay R6 is not energized, but the fifth relay R5 is energized and the third modulator i3 is unbalanced, and the Sign of the first sideband lter d5 is of no consequence. The first bank 'i5 of decade C is connected to the rst input terminal 3l of the third modulator 43 through the first switch |05 controlled by the sixth relay R6. Decade C is set on O, so that P is 0, due to the condition of the switches |03 and i041 of the fth relay R5. The second |04 of these switches effects the unbalancing of the second modulator Q2, and the sign of the-second sideband lter 50 is also of no consequence. The third relay R3 is notenergized. The rst switch bank 'i3 of decade Bis connected to the input terminal 36 of the second modulator 42 through the rst switch 95 of the third relay R3. Decade B is set on 1, so that N is 9 (which is 1'0-1) and the consequences of `relay R2 being energized are none for the two switches 93 and 94 thereof are in the circuit only whendecade Bis set on zero. The first and third relays RI and nR3 are energized; however, so `that the. sign'of `the third sideband 'filter '.55 is Since thesign :of .thesecond'sideband filter 50 is 'of/no consequence, 'energization Yof the third relayR3 .has :no veffect on thisoperation. The secondfswitch bank of decade A Ais connected to the input terminal 35 .of the first modulator di through the Viirst switch .9| of thethird relay R3. Decade A isset-on 4, so that M is 5 (which is lei-l). The 'harmonics that are combined Vto synthesize 41.00 .md/sec. are then,.in `accordance with Relation 1,

50-[9-1-(04-0) 1:41.00 Inc/sec.

The separation in this case is 18 Inc/sec., which is veryfgood.

As pointed out above, the'separation of the sum and difference frequencies furnished byany one ofthe modulators 41,42, or GB-,should be at least as greatas the'spread between'two adjacent harmonic orders of the higherdecade'frequencygenerator t0, .I l, I2, Vor 13 employed to actuatetl'ie modulator. For example, where tenthsand hum dredths are combined in a modulator, -thesum and difference frequencies should be Yat least a tenth of a megacycle part; or, when tens and units are combined, the .sumtnd difference frequencies should be at least ten megacycles apart. Separation inthe sideband i'llters is then readily accomplished. In the first-example given above, the separation between the sum and difference frequencies furnished when 0.7 and 0.07 mc./sec. are `'combined is which is greater Vthan'ul The separation between the Vsum and difference frequencies furnished when .8.0 and0.63-mc./sec. are combinedis which Yis greater than 1.0. The separation between the sum and difference .frequencies furnished when 20 and 8.63'mc./sec. are .combinedis which isg'greater-,than;10. 4Inthesecond example, the separation betweenr59vand .41 mc./sec. is ,18 mc./sec., which again is greater than .10. .Theapparatus is designed to yield Vin each case aseparation which, though it Ymay in a particular vcase be-equalled, cannot `be improved upon.

Many modications .and variations of .thisinvention-will occur to those skilled in theart, for the particular frequency generator shown in Fig. 1 and harmonic-computer shown in Fig. 2 illustratecnly one .examplefof how .the invention may be practiced.

For example, the computer of Fig. 2 may .be arranged A,so that each of the terminals of the various harmonic selector switches is-connected to a lamp that is provided with anindcator to show the frequency .that is being selected,.instead of beingconnected directlyto the `frequency generator. If the lsideband filter terminals `46, 4l, 5|, 52, 56 and Bland the vunha-lanceterminals 6|, B2 and 63'of VVthe computer are likewise arranged, the solution to any frequency synthesis problem that can be set `up on the computer -will'be indicated by illuminated'charactersand signs. illust solution may .then be used asdesired. `Further, the rfour decades A, BA1-and vD may be operated by a telephonedial-and stepping switchesfwell known to the telephone art, so that the setting up of a desired frequency-then involves only the dialingv of the digits :of that frequency. Still rfurther, the numberrofdigits ina frequency sought .to Ybe quency.

synthesized by means of a computer in accordance with this invention is not limited to four; it may be any number greater or lesser. The computer may be constructed with more or fewer decades A, B, C, or D, it being particularly noteworthy that decades B and C are similar, and more like them may be added. All that is required is to set up the necessary rules for frequency synthesis in accordance with the method set forth herein, and to construct the switching circuits in accordance with these rules. Actually, the decade system is not the only system that can be used, although it is thev most convenient. A system based on any other number grouping may be used if desired, for example a system in which eights instead of tens are the basis from which harmonics are generated. However, a system of tens offers the greatest simplicity, since it so closely resembles the decade system used in numerical representation.

The invention may have particular commercial value, for example, in the taxicab or trucking business, where each Vehicle in the field may have a receiver and transmitter set up on an individual frequency, and the main oihce may have a transmitter and receiver that is automatically tunable to a master oscillator fre- 'I'hen a computer in accordance with the invention, if equipped with a telephone dial, may be used to control a frequency generator like that shown in Fig. l, which in turn may be used as the master oscillator, to enable the main oiilce to call any vehicle in the field in the same manner as one places a dial telephone call.

It is therefore desired that the appended claims shall be given a broad interpretation commensurate with the scope of the invention within the art.

Vlhat is claimed is:

l. In the generation of a frequency AB cycles per unit time, where A and B are digits, by the combination of two individual frequencies M and N in the manner MiN, a switching system for automatically selecting values of said individual frequencies M and N and the algebraic sign (-1-) or comprising rst switch means having a plurality of circuits making contacts for selecting the first individual frequency M when set on one contact in accordance -with the first digit A, second switch means having a plurality of circuits making contacts for selecting the second individual frequency N when set on one contact in accordance with the second digit B, and relay operated switch means controlled by both said rst and second switch means and arranged to select said algebraic sign or in accordance with the settings of both said rst and second switch means, both said first and second switch means being arranged so that at all times the difference between M-l-N and M N is at least as great as the difference between the frequencies (Ail) B and AB, where (Ail) B is the frequency AB changed by one digit in the first place.

2. In the generation of a frequency AB cycles per unit time, where A and B are digits, by the combination of two individual frequencies M and N in the manner MiN, a switching system for automatically selecting values of said individual frequencies M and N and the algebraic sign or comprising first switch means having a plurality of circuit-making contacts for selecting the first individual frequency M when set on one contact in accordance with the rst digit A,

second switch means having a plurality of circuit-making contacts for selecting the second individual frequency N when set on one contact in accordance with the second digit B, first relay operated switch means controlled by said sec'- ond switch means and arranged to condition thev selection of said first switch means in accordance with the setting of said second switch means, and second relay operated switch means controlled by both said first and second switch means and arranged to select said algebraic sign (-1-) vor in accordance with the settings of both said first and second switch means, both said rstand second switch means being Varranged so' that at all times the difference be-v tween M -l-N 'and M N is at least as greatl as the difference between the frequencies (Ail) B` is the frequency AB changed by one digit in the, rst place.

3. In combination with a frequency generator which is adapted to generate a frequency AB cycles per unit time, where A and B are digits,A by the combination of two individual frequencies M and N in the manner MiN, a switching system' for automatically conditioning saidv generator to provide said individual frequencies M and N with a predetermined sign (-1-) or comprising first switch means having a plurality of circuitmaking contacts connected to said generator and adapted to condition said generator to provide the first individual frequency M when set on one contact in accordance with the nrst digit A, second switch means having a plurality of circuitmaking contacts'conne'eted to said generator and adapted to condition said generator to provide the second individual frequency N when set on one contact in accordance with the second digit B, and relay operated switch means controlled by both said first and second switch means and connected to said generator and adapted to condition said generator to combine said individual' frequencies M and N either additively or subtractively in accordance with the settings of both said first and second switch means, both said rst and second switch means being arranged so that at all times the difference between M +N and M -N is at least as great as the difference between the frequencies (Ail) B and AB, where (Ail) B is the frequency AB changed by one digit in the rst place.

4. In the generation of a frequency AB cycles per unit time, where A and B are digits, by the combination of two individual frequencies M and N in the manner MiN, apparatus for choosing most advantageous values for M and N which comprises means settable in accordance with the rst digit A for relating M to A in one of four fashions, M A, M :A4-1, M=l0-A, or M=l0 (A-}l); means settable in accordance wtih the second digit B for relating N to B in one of four similar fashions, N=B, N=B|1. N=10-B, or N=10-(B|1) and means responsive to the settings of said settable means to select the algebraic sign between the M and N as selected by said settable means, said settable means being constructed and arranged to select values of M and N such that either M +N or M N yields the frequency AB cycles per unit time and the separation between M -l-N and M N is a maximum.

5. In the generation of a frequency ABCD cycles per unit time where A, B, C, and D are digits by synthesis from four frequencies M, N, P, and Q which are respectively harmonic orders of four basic frequency generators that are related to each 'other in decade fashion in the manner M- f-[N- f-(P- tQlL apparatus for choosing the most advantageous values for M, N, P, and Q and the most advantageous algebraic signs which comprises means settable in accordance with the iirst digit A for relating M to A in one of four fashions M=A, M=A|l, M=l0-A, or M=lO- A+1) means settable in accordance with the second digit B for relating N tc B in one of four similar fashions N=B, `N=15l1, N='10-B, or N=10-(B-{1); means settable in accordance with the third digit C for relating P to C in one of four similar fashions P=C, R=C-|-1, P=10-C, or P=l0 (C4-l) means settabl'e in accordance with the fourth digit D for relating Q to D in one of four similar fashions QZD, Q=D+1, Qzloab, or Q=10 D+1); and means responsive to the settings of said settable means to select the algebraic sign between P .and Q asset by .said C and D .settable means, lbetween Pi@ Vand N as set by said B settable means, and between (PQDN and M as 'set by said .A settable means, said sett-able means being constructed and arranged to select values of M, N, P, and Q which provide the maximum separation between the sum and the dif-- ference in each algebraic operation, and said algebraic sign setting means being constructed and arranged to provide that the algebraic sign in each position shall be plus when the harmonic order M, N, or P preceding that vsign is equal to the corresponding digit A, B, or C respectively or 10-l (that digit-i-l), and minus when said harmonic order is equal to the corresponding digit +1 or 10- (the corresponding digit).

6. In combination with a frequency generator which is adapted to generate a frequency AB cycles per unit time, where A` andB are digits, by the combination of two individual frequencies M and N in the manner M iN, a balanced modulator wherein said individual frequencies are combined to produce the frequencies M +N and M -N, `means in circuit with said modulator for selecting one of said products, and means in circuit Wth said modulator for causing the unbalance thereof, a switching system connected to said generator and modulator and governing the operation thereof comprising first switch means having a plurality of circuit making contacts connected to said generator and adapted to condition said generator to provide the rst individual frequency M when set on one contact in accordance with the rst digit A, second switch means having a plurality of circuit-making contacts connected to said generator and adapted yto condition said generator to provide the second 'individual frequency N when setxon one lcontact in .accordance with the second digit B, iirst relay operated switch means controlled by said .switch means and connected to said modulator and adapted to condition said modulator to combine said individual frequency M and Neither additively or subtractively in accordance with the setting of both iirst and second switch means, and second relay operated Switch means controlled by said first and second switch means and connected to the unbalancing means of said modulator, and arranged to unbalance said modulator when one of said digits is zero.

KENNETH A. YOUNG.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,131,558 Granger Sept. 27, 1938 2,231,634 Monk Feb. 11, 1941 2,401,694 Bligh et al June 4, 1946 '2,450,696 Stenning Oct. 5, 1948 

